1. Field of the Invention
The present invention relates to a piezoelectric element, an ink jet recording head using such a piezoelectric element and a method for manufacturing such a piezoelectric element.
2. Related Background Art
A piezoelectric element is constituted by piezoelectric ceramic having a ferro-dielectric or para-dielectric property. Composition of the piezoelectric ceramic is generally comprised of a two-component system mainly including titanic acid zirconium acidic lead (referred to as “PZT” hereinafter) or a three-component system in which a third component is added to PZT of the two-component system. The ferro-dielectric member using PZT of the two-component system is disclosed in “Applied Physics Letters”, vol. 58, No. 11, pp 1161–1163, published on 1991.
As methods for manufacturing a ferro-dielectric film of metal oxide type, there are a spattering method, an MOCVD method, a sol-gel method and the like. The sol-gel method is a method in which solution including compound capable of performing hydrolysis of various component metals as raw material and partial hydrolysis substance or partial polycondensation substance thereof is coated on a substrate and the coating is dried and, thereafter, the substrate with the coating is heated in an air environment to form a metal oxide film and further the sintering is performed at a temperature greater than a crystallizing temperature of the metal oxide to crystallize the film, thereby forming a ferro-dielectric film. As the metal compound capable of performing the hydrolysis of the raw material, organic compound such as metal alkoxide, partial hydrolysis substance or partial polycondensation substance thereof is generally used. The Sol-gel method can form the ferro-dielectric film most easily in a most inexpensive manner. As a method similar to the sol-gel method, there is an organic metal decomposing method (MOD method). The MOD method is a method in which solution including thermally decomposable organic metal compound such as β-diketone complex or carboxylate is coated on a substrate and the substrate and the coating are heated in an air or oxygen environment, for example, to evaporate solvent in the coating and to thermally decompose the metal compound thereby to form a metal oxide film and the sintering is performed at a temperature greater than a crystallizing temperature to crystallize the film. In this specification, the sol-gel method, MOD method and a combination thereof are generically referred to as “sol-gel method”. Further, a printer head of ink jet type utilizing a piezoelectric element formed by the sol-gel method is also disclosed. For example, in Japanese Patent Application Laid-Open Nos. H09-92897, H10-139594 and H10-290035, there is disclosed a method in which a piezoelectric film of a piezoelectric element used in a printer head of ink jet type by repeating the coating of sol including piezoelectric material onto a lower electrode and the heat treatment of the coating by several times.
Further, a method for manufacturing the piezoelectric element to improve a close contact ability by forming a mixture layer in which crystal structures are formed between an electrode and a piezoelectric film is disclosed (for example, refer to Japanese Patent Application Laid-Open No. 2000-79689).
As disclosed in the above-mentioned Japanese Patent Application Laid-Open Nos. H09-92897, H10-139594 and H10-290035, in the past, in order to enhance performance and endurance of the printer head of ink jet type, various techniques for enhancing a property and reliable operation of the piezoelectric element used as an actuator have been proposed. As a multi-crystal structure of the piezoelectric material by the sol-gel method, a columnar structure is known. The columnar structure is a structure in which grain boundary is formed substantially in perpendicular to a film thickness and a surface thereof certain unevenness in accordance with a grain size. This structure creates interfacial roughness between the structure and an upper electrode, which leads in increase in leak current and deterioration of a piezoelectric property. Further, in the conventional piezoelectric element, if noble metal such as Ru or Pt or oxide thereof is used as the lower electrode, due to out of alignment of the interface between the piezoelectric film and the lower electrode, there arises a problem regarding reduction in an electrical property, i.e. increase in leak current and in reduction in dielectric breakdown resistance. Further, if oxide of conductive perovskite type is used as the lower electrode, since the resistance value of the electrode is great in comparison with noble metal, there arises a problem regarding reduction in the property of the piezoelectric film, particularly reduction in a displacement amount. Further, in the method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2000-79689, since the electrode does not have the perovskite structure, crystal in the piezoelectric film is disturbed at the interface between this film and the piezoelectric film having the perovskite structure, thereby deteriorating the property of the piezoelectric film.